Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$55.63	9.128%	$60.7079	$60.71	$60.70	$60.70
Purchase #2	$85.78	5.364%	$90.3812	$90.38	$90.40	$90.40
Purchase #3	$99.26	12.467%	$111.6347	$111.63	$111.65	$111.60
Purchase #4	$103.55	9.294%	$113.1739	$113.17	$113.15	$113.20
Purchase #5	$65.75	13.381%	$74.548	$74.55	$74.55	$74.50
Purchase #6	$51.36	5.607%	$54.2398	$54.24	$54.25	$54.20
Purchase #7	$205.47	5.687%	$217.1551	$217.16	$217.15	$217.20
7 purchase totals =	$666.80		$721.8406	$721.84	$721.85	$721.80